Refinement and application of a regional atmospheric model for climate scenario calculations of Western Europe

The KNMI regional climate model RACMO is increasingly used in the refinement of climate scenarios. Examples include heat waves, in particular their frequency and intensity, the occurrence of local extremes in precipitation, and wind storms. In this project a number of components within RACMO have been further developed. The existing boundary-layer scheme has been extended with a prognostic variable for turbulent kinetic energy to improve the representation of a developing boundary layer. This modification turns out to be beneficial for the representation of the stable boundary layer. The soil hydrology component of the model is further refined by introducing spatial heterogeneity into a number of soil hydrology parameters, e.g. soil type and maximum root depth, which results in spatially more prominent structures at the regional scale. The new model formulation has been extensively tested at the European scale against daily observations of temperature and precipitation. In addition, RACMO has been coupled to the chemistry-transport model LOTOS-EUROS. A module has been incorporated in RACMO to account for the effect of aerosols to the cloud radiation interaction, the so called first aerosol indirect effect. Parallel to the model development, the existing model version has been used in various applications, e.g. quantification of the effect of anomalously high North Sea temperatures in summer to the intensity of precipitation over land and the role of temperature in the analysis of extreme precipitation at a daily and hourly scale. A special application regarded a contribution to the Delta Committee, which dealt with the distribution of heaviest storms over the North Sea as simulated by the model in the present-day climate and in a future climate.